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Air Conditioning Repair FAQ: How to Diagnose & Repair Air Conditioners InspectAPedia®  -     Detailed air conditioner diagnosis & repair checklist How to diagnose & repair most air conditioning system problems Air conditioner compressor defect diagnosis

This Air Conditioning Troubleshooting & Diagnosis FAQ (list of frequently asked questions about air conditioners) lists the major areas of investigation to be followed in diagnosing all types of problems with air conditioning systems and air conditioning equipment.

Typical air conditioner concerns include compressor or blower assembly noises, failure of air conditioners to start or to keep running, inadequate cool air flow or air quantity, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely. Also discussed are various electrical wiring, fusing, overcurrent, and thermostat or control defects on air conditioners.

Here are the Major Areas to Investigate for Problems With Air Conditioning Systems & Equipment

• SYSTEM OPERATION what are the basics?
• OPERATING CONTROLS what and where are the various air conditioner controls & switches?
• SAFETY CONTROLS what safety controls and switches are required on air conditioners?
  
  
• OPERATING TEMPERATURES how & where to measure central air conditioning temperatures
  
  
• OPERATING DEFECTS
• The air conditioning system will not operate at all: power may be off, controls may be improperly set, or the system may be inoperative. (Confirm that the system has electrical power and that all of its control switches and thermostat are set to "on" and "cooling" positions.
  See CONTROLS & SWITCHES
  
• The air conditioning system operates but does not produce cool air, or not enough cool air.
  See LOST COOLING CAPACITY
• The air conditioning system operates but there is not enough cool air flow at the registers.
  See DUCT SYSTEM DEFECTS.
• The compressor was short-cycling, that is, turning itself on and off rapidly, perhaps every few seconds or minutes rather than producing a normal on-cycle of 10 minutes or longer.
  See COMPRESSOR CONDENSER
• The compressor was noisy, during startup, indicating an operating problem.
  See COMPRESSOR NOISES.
• The compressor squealed at startup, indicating that service may be needed promptly to prevent possibly costly damage to the system. This repair/maintenance item should not be deferred.
  See COMPRESSOR NOISES.
  
• Inside cooling or evaporator coil defects that can be seen by eye: dirty coil, blocked coil, frost on the coil, improperly sized evaporator coil, improper evaporator or cooling coil placement in the system.
  See AIR HANDLER UNIT.
• Air flow across the air conditioning evaporator coil: if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty blower squirrel cage fan), the air conditioning system will not operate properly.
  
  Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity.
  
  One ton = 12,000 BTUH so if your AC unit is a 24,000 BTUH unit it is a "two ton" unit and needs to see 700 to 800 CFM of air across the evaporator coil.
  
  Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy.
  
  The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.
  
  See COOLING COIL or EVAPORATOR COIL and also DIRTY COOLING COIL - how dirt and debris appear, what to do about a dirty evaporator coil.
  
  Evaporator coil cleaning often requires cutting refrigerant lines, removal of the coil and other components for cleaning, and reinstallation, pulling a vacuum on the refrigerant lines, and recharge with refrigerant. Such service and repair may involve significant expense, although there are some "in place" cleaning methods using foams and sprays that are a simpler procedure.
  See DIRTY COIL CLEANING PROCEDURES, FROST BUILD-UP and OPERATING TEMPERATURES.
  
  
• Dirty air conditioning filters, - a source of increased operating costs. Very dirty filters can eventually block the fan itself, leading to more costly repairs. The filters should be changed monthly when the system is in use. Failure to properly filter dust from the return air supply can load the fan or evaporator coil with dust and prevent proper system operation. Installing a filter is normally a minor expense. Dirty, blocked evaporator coils can result in improper system operation, very low output temperatures, low air flow (compensated sometimes by increased fan speed), and sometimes frost on the coil and failure of system components.
  See AIR FILTERS for HVAC SYSTEMS, and also AIR HANDLER UNIT. See OPERATING TEMPERATURES.
  
  
• The air conditioner operates but our electrical bills are too high.
  See DIRTY COIL CLEANING PROCEDURES, SEER RATINGS and see DUCT SYSTEM DEFECTS.
  
  
• The air conditioner fuse keeps blowing or the circuit breaker trips: could mean a compressor which needs repair or replacement, or it could mean a problem with the unit's electrical wiring, such as use of aluminum wiring combined with bad electrical connections. Have your service technician check the condition of the electrical circuit first (that's cheaper than a new air conditioning compressor) and then check the condition of the compressor.
  See COMPRESSOR CONDENSER for air conditioner compressor diagnosis and repair; and if your air conditioning system electrical wiring is aluminum, review the aluminum wiring hazards at ALUMINUM WIRING HAZARDS & REPAIRS since a serious fire hazard could be present.
  
  
• LOST COOLING CAPACITY explains how to diagnose & repair an Air Conditioner system which has lost cooling capacity
  
  
• COMPRESSOR CONDENSER which describes problems with air conditioner compressor/condenser units
• INSTALLATION ERRORS
• CONDENSING COIL FINS, SUPPORT PADS
• COMPRESSOR NOISES - diagnosing and curing a noisy air conditioner compressor unit
• HARD STARTING - how to fix an air conditioner compressor motor that won't start
• TIGHT or SEIZED AC COMPRESSORS - how to diagnose a compressor that needs replacement
• COMPRESSOR PRESSURE READINGS - what are the usual system pressures in an air conditioner or heat pump?
• BURNED-OUT COMPRESSOR - how we diagnose a compressor motor that is burned out
• REPLACING A COMPRESSOR - steps in installing a new air conditioner compressor
• A/C CAPACITORS - using starter capacitors on an air conditioner compressor or other electric motors
  
  
• AIR HANDLER UNIT which describes problems with the air handler, air filters, and the cooling coil itself
• DIRTY A/C BLOWERS
• Leaks, Rodents In Air Handlers
• Mold Growth in Air Handlers
• DIRTY COOLING COIL
• FROST BUILD-UP
• BLOWER LEAKS, RUST & MOLD
• ADDING A/C: RETROFIT SIZING
  
  
• AIR FILTERS for HVAC SYSTEMS - air filters are critical not only for building health and comfort but to keep an adequate air volume moving through the air conditioning or heat pump system
• Air Filter Location - where should air filters be located
• Dirty Air Filter Problems - what happens when the air filter gets dirty - how often should filters be changed?
• Missing Air Filters - what happens if we simply omit the air filter - some costly problems develop
• OPTIMUM INDOOR AIR FILTERS - what is the absolute best, most effective way to clean indoor air
• Air Filter Efficiency - MERV and other air filter ratings
• Optimum Air Filter Design / Location
• How to Cascade Air Filters
• AIR FILTER EFFECTIVENESS - what determines how effective an air filter will be
• MERV, HEPA Definitions
• MERV Air Filter Ratings
• How Air Filters Work
• Particle Sizes & IAQ
• Gasketed air filters
• Debris in Return Air Plenum
• Washable air filters
• FIBERGLASS & AIR FILTERS - how these filters work
• Air Filters Shed Fibers? - are there problems with air contamination?
• Fiberglass & Test Lab Accuracy
• Variations in Fiber Size
• SOURCES FOR AIR FILTERS - where to obtain air filters of various sorts
• OTHER AIR CLEANERS - how effective are other air cleaners such as free-standing air purifier units? Are some of them dangerous? Maybe. Are claims exaggerated? Usually.
  
  
• CLEANING & Legionella BACTERIA how to remove or prevent bacterial growth in air conditioning systems, cleaning condensate trays, cooling towers, use of chlorine, bromine, disinfectants in air conditioners
  
  
• CONDENSATE HANDLING
• DRIP TRAY DEFECTS can cause leaks into a building interior and may be a mold source
• CONDENSATE LEAKS
• CONDENSATE PUMPS, where and how to use them
• CONDENSATE DRAINS, proper routing and potential health concerns
  
  
• COOLING COIL or EVAPORATOR COIL - problems at the evaporator coil can cause total loss of cooling capacity (or heating with a heat pump)
  •  DAMAGED COOLING COIL
  • DIRTY COOLING COIL - how dirt and debris appear, what to do about a dirty evaporator coil
  • DIRTY COIL CLEANING PROCEDURES - a review of methods for cleaning a dirty A/C coil
  • FROST BUILD-UP - the cause and cure of ice on the A/C cooling coil
    
    
• DUCT SYSTEM DEFECTS which describes problems with the duct system.
• SUPPLY REGISTERS, & ZONES, how to inspect for defects
• RETURN AIR REGISTERS & DUCTS , how to inspect for defects
• BALANCING AIR DUCT FLOW, how to balance the air flow in a heating or cooling system
• UNDERSIZED RETURN DUCTS, how to recognize under-sized air conditioning ducts or inadequate return air
• INCREASING RETURN AIR, poor air flow cause and cure, how to increase return air and thus cooling air flow
• LOCATION OF REGISTERS & DUCTS, improper placement can reduce air conditioning capacity or may be unsafe
• DUCT ROUTING & SUPPORT errors in duct routing and support can cause poor air flow or air quality and mold problems
• WET CORRODED DUCT WORK, water and rust as indicators of duct conditions, possible mold or other pathogenic health hazards
• LEAKY DUCT CONNECTIONS, how to diagnose and correct leaky ducts
• VIBRATION DAMPERS and asbestos hazards at the air conditioner air handling unit or blower
• GOODMAN GRAY FLEXDUCT deterioration of flex duct, cause, cure
• OWENS CORNING FLEXDUCT deterioration of flex duct, cause, cure
• UNSAFE DUCT OPENINGS as a possible source of air quality issues or carbon monoxide poisoning hazards
• ASBESTOS HVAC DUCTS how to recognize asbestos materials on heating and cooling air ducts and equipment
• Transite Pipe HVAC Ducts as a possible source of asbestos, blocked ducts, reduced air flow, mold
• FIBERGLASS HVAC DUCTS fiberglass contamination of indoor air, fiberglass as a possible mold source
  
  
• REFRIGERANTS in AIR CONDITIONERS & HEAT PUMPS:lists historic and currently in-use air conditioning refrigerants and gives their characteristics
  • REFRIGERANT LEAK DETECTION - how to find where refrigerant gas leaks are happening
  • REFRIGERANT LEAK REPAIR - how to fix air conditioning or heat pump refrigerant gas leaks

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING SYSTEMS.

If your air conditioning system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

• CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
• OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
• LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
  • What to check first if there is no cool air or not enough cool air
  • Compressor failure diagnosis: basic checks of the air conditioner compressor
  • Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems
• COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
• AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
• DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
• A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
• A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair

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AIR CONDITIONING & HEAT PUMP SYSTEMS
AGE of AIR CONDITIONERS & HEAT PUMPS
AIR CONDITIONER BTU CHART
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR CONDITIONER NOT WORKING
AIR FILTERS for HVAC SYSTEMS
AIR HANDLER UNIT
BACKUP HEAT for HEAT PUMPS
BLOWER DOORS & AIR INFILTRATION
BOOKSTORE - Air Conditioning "How To" Books
CLEANING & Legionella BACTERIA
COMPRESSOR & CONDENSING COIL
CONDENSATE HANDLING
CONTROLS & SWITCHES
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
DATA TAGS on AIR CONDITIONERS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DUCT SYSTEMS
DUCTS - Asbestos
DUCT SYSTEM DEFECTS
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCTS, Asbestos Transite Pipe
DUST FROM HVAC?
ENERGY SAVINGS in BUILDINGS
EVAPORATIVE COOLING SYSTEMS
FAN AUTO ON Thermostat Switch
HEAT LOSS (or GAIN) in BUILDINGS
HUMIDITY LEVEL TARGET
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS
LOST COOLING CAPACITY
MOTOR OVERLOAD RESET SWITCH
OPERATING COST
OPERATING DEFECTS
OPERATING TEMPERATURES
REPAIR GUIDE for AIR CONDITIONERS
REPAIR & DIAGNOSTIC FAQs for A/C
REFRIGERANTS
SEER RATINGS & OTHER DEFINITIONS
SYSTEM OPERATION
SWAMP COOLERS
THERMOSTATS
THERMOSTATIC EXPANSION VALVES
CRITICAL DEFECTS
Air Conditioning "How To" Books

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.
• Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
• Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
• "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
• Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
• ...
  

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